Ultrasonic transit time measurements will be used to continuously record fetal head descent and rotation as well as curvical dilatation during labor. Low duty cycle ultrasonic pulses will be used to minimize net irradiation of the fetus and mother. Transit times will be measured by a pulse delay time technique or if increased resolution is required, frequency modulation will be applied to the ultrasonic pulses. Transmitting transducers will be located on the maternal pelvic region, and the receiving transducers will be attached to the fetal head and cervical lip. Transit time measurements will give displacements between transmitting and receiving transducers which will then be analyzed by triangulation techniques on a digital computer.